1. Field of the Invention
The present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic pressure supply system of an automatic transmission for a vehicle which can improve safety and reliability as a consequence of operating a high-pressure hydraulic pump by driving torque of an engine when the high-pressure hydraulic pump does not operated due to failure of the high-pressure hydraulic pump.
2. Description of Related Art
Recently, vehicle makers direct all their strength to improve fuel economy due to worldwide high oil prices and strengthen of exhaust gas regulations.
Improvement of fuel economy may be achieved by improving power delivery efficiency in an automatic transmission, and improvement of the power delivery efficiency may be achieved by minimizing unnecessary power consumption of a hydraulic pump.
A recent automatic transmission is provided with a low-pressure hydraulic pump and a high-pressure hydraulic pump so as to improve fuel economy. Therefore, hydraulic pressure generated by the low-pressure hydraulic pump is supplied to a low pressure portion (i.e., a torque converter, a cooling device, and a lubrication device), and hydraulic pressure generated by the high-pressure hydraulic pump is supplied to a high pressure portion (i.e., friction members selectively operated when shifting).
In further detail, general hydraulic pressure of the automatic transmission is generated for the low pressure portion (i.e., generated by the low-pressure hydraulic pump), and hydraulic pressure demanded by the high pressure portion is generated by the high-pressure hydraulic pump and then is supplied to the high pressure portion.
Since power consumption for driving the hydraulic, pumps can be minimized, fuel economy may be enhanced. In addition, since a load applied to the hydraulic pumps is reduced, noise and vibration may be reduced and durability may be improved.
In a conventional hydraulic pressure supply system, the low-pressure hydraulic pump and the high-pressure hydraulic pump are driven by one drive shaft or the low-pressure hydraulic pump is driven by driving torque of an engine and the high-pressure hydraulic pump is driven by driving torque of a motor.
In a case that the low-pressure hydraulic pump and the high-pressure hydraulic pump are driven by one drive shaft, however, it is impossible to control rotation speeds of the low-pressure hydraulic pump and the high-pressure hydraulic pump independently. In addition, since the high-pressure hydraulic pump discharges the maximum pressure demanded by a transmission, unnecessary power loss may occur.
On the contrary, in a case that the low-pressure hydraulic pump is driven by the driving torque of the engine and the high-pressure hydraulic pump is driven by the driving torque of the motor, the motor may not operate due to failure of the motor or lack of SOC of a battery
In this case, the hydraulic pressure is not supplied to the high pressure portion and the transmission may be damaged.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.